1. Field of the Invention
The present invention relates to a selective etching method for a stacked organic film, and in particular to an improved selective etching method for a stacked organic film which is capable of effectively removing an organic anti-reflection layer without a loss of a photoresist film before etching a base layer such as a wafer, etc., by using an organic anti-reflection layer.
2. Description of the Conventional Art
Recently, during the etching process for fabricating a semiconductor device, an anti-reflection bottom organic layer is increasingly used in order to increase the depth of an optical focus (DOF) and resolution at the time of using an i-Line/DUV (Deep UV) photoresist (PR) film.
The composition of a commercially-used organic anti-reflection layer is different based on the fabrication company and the kind of a photoresist (PR) film, but includes aromatic agents of which carbon is a major element. The etching characteristic of a bottom organic anti-reflection layer is very similar to the etching characteristic of the photoresist film. In particular, an isotropic etching profile may be formed under an oxygen (O.sub.2) plasma at room temperature due to a chemical etching characteristic of a photoresist film and bottom organic layer, which characteristic is directed to forming a main product of CO.sub.2 without using gas, for thus causing a large critical dimension (CD) bias. Therefore, in the conventional art, N.sub.2, Ar, SO.sub.2, etc. or CF.sub.4, CHF.sub.3, C.sub.2 F.sub.6, etc. which are compound gases including fluorine are added, and then the organic anti-reflection layer is etched. A polymer such as CN.sub.X, CS.sub.X, CF.sub.X, CHF.sub.X, etc is formed at a sidewall of the organic anti-reflection layer which remains after the etching process, and the anisotropic etching profile of the organic anti-reflection layer is maintained, and the residual organic anti-reflection layer and a critical dimension (CD) bias of the photoresist layer are minimized.
FIGS. 1A through 1C illustrate a conventional selective etching method of a stacked organic film.
As shown in FIG. 1A, a first organic film 13 such as an organic anti-reflection layer is coated on the upper surface of a base layer 11 which becomes an etching object layer, and a second organic film 15 such as a photoresist film patterned for etching the base layer 11 is formed on the upper surface of the first organic film 13. The thusly patterned second organic film 15 is used as a mask at the time of etching the base layer 11. As shown in FIG. 1B, a passivation gas such as CF.sub.4, CHF.sub.3, N.sub.2, etc. is added into an O.sub.2 plasma before the base layer 11 is etched. However, at this time, the second organic film 15 is etched and eroded together with the first organic film 13, and the second organic film 15 is changed to a triangle-shaped second organic film 15a. A sidewall passivation film 17 is formed on sidewalls of the first organic film 13a formed below the second organic film 15a by CF.sub.4, CHF.sub.3, N.sub.2, etc. Thereafter, as shown in FIG. 1C, the base layer 11 is etched by using the second organic film 15a as a mask, and then the first organic film 13a including the second organic film 15a and the sidewall passivation film 17 are removed, for thereby finishing the etching process. The anisotropic etching profile of the first organic film is maintained by the sidewall passivation film 17, and the critical dimension biases of the first organic film 13a and the second organic film 15a are minimized. However, since the etching speed ratio between the second organic film 15 and the first organic film 13 is similar, the second organic film 15 is eroded together with the first organic film 13 at the time of etching the first organic film 13, so that the etching is first performed at a corner portion of the same, for thus forming a much deformed profile of the second organic film 15a. Therefore, when etching the base layer 11 by using the deformed second organic film 15a as a mask, as shown in FIG. 1C, a narrowed upper portion, widened lower portion and sloped pattern of the base layer 11a is formed.
The problems of the conventional selective etching method for a stacked organic film will now be explained.
First, when etching the first organic film such as an organic anti-reflection layer, an ion sputtering effect is increased due to heavy gases having a large molecular structure such as SO.sub.2, CHF.sub.3, C.sub.2 F.sub.6, etc., whereby the second organic film such as the photoresist film is severely eroded. Therefore, when etching the base layer (the etching object layer) by using the thusly deformed second organic film as a mask, it is impossible to maintain a desired profile of the base layer.
Second, since the etching speed ratio between the second organic film and the first organic film is similar, the loss of the second organic film is much increased at the time of etching the first organic film. Therefore, when etching the base layer, since the second organic film does not play the role of a mask, the base layer may be attacked.
Third, since an organic polymer (sidewall passivation film) such as CF.sub.X, CHF.sub.X, etc. is formed on the base layer, the sidewall passivation film acts as a barrier at the time of etching the base layer.